The market for carbon dioxide (CO2) is wide ranging and includes food production, enhanced oil recovery, methanol production etc. One source for carbon dioxide is ethylene glycol plants. The production of ethylene glycol involves the oxidation of ethylene, which can produce CO2 streams as a by-product (off-gas). These CO2 streams, typically, are contaminated with organic chlorides, saturated and unsaturated hydrocarbons, and water.
In contemporary CO2 purification plants having a CO2 feed stream from an ethylene glycol plant, the CO2 feed stream, which contains saturated and un-saturated hydrocarbons along with one or more organic chlorides, undergoes a catalytic oxidation process using a noble metal catalyst in the presence of excess oxygen. The catalytic oxidation process oxidizes organic chloride, which leads to the formation of hydrochloric acid (HCl). Hydrochloric acid is corrosive and causes corrosion of equipment, such as heat exchangers, that are downstream from the catalytic oxidation process that forms the hydrochloric acid.
FIG. 1 provides an illustration of such a prior art system 10. In FIG. 1, CO2 feed stream S100 is fed to multi-stage compressor 100. Multi-stage compressor 100 performs multi-stage compression of CO2 feed stream S100 to form compressed CO2 feed stream S101. This multistage compression of CO2 feed stream S100 removes some of the water from CO2 feed stream S100. The multistage compression of CO2 feed stream S100 also causes compressed CO2 feed stream S101 to have a higher pressure and temperature than CO2 feed stream S100. Compressed feed stream S101 is flowed to heat exchanger 101, which heats compressed CO2 feed stream S101 to form hot CO2 stream S102. Hot CO2 stream S102 is at a temperature and pressure sufficient to facilitate catalytic oxidation of the saturated and unsaturated hydrocarbons and organic chlorides in catalytic oxidation reactor 102. The catalytic oxidation reactions in catalytic oxidation reactor 102 oxidize the saturated and unsaturated hydrocarbons and organic chlorides and thereby form CO2, water (H2O), and HCl. Catalytic output stream S103 of catalytic oxidation reactor 102 is passed through a series of heat exchangers, represented in FIG. 1 as heat exchanger 103, which condenses gaseous HCl and water vapor to form liquid HCl in stream S104. Stream S104 is flowed to HCl absorber 104 where HCl is absorbed. The HCl formed in the catalytic oxidation process causes dew point corrosion in equipment downstream of catalytic oxidation reactor 102, which can result in equipment failure and shutdown of the CO2 purification operation. The equipment that may be most susceptible to HCl corrosion is equipment, such as heat exchanger 103, that is downstream catalytic oxidation reactor 102 but upstream HCl absorber 104. It should be noted, however, that, if HCl absorber 104 is ineffective (e.g., due to malfunction), the equipment downstream of HCl absorber 104 may also be subject to HCl corrosion.
Some prior art methods for addressing the issues of HCl corrosion downstream of a catalytic oxidation reactor involve upgrading the metallurgy of heat exchangers downstream of the catalytic oxidation reactor where the dew point corrosion is at its highest level. However, this is an expensive practice.
Another prior art method for addressing the issue of HCl corrosion of equipment involves atomizing NH3/amines in a process stream so that the NH3/amines neutralizes the HCl formed at the dew point in the catalytic output stream. However, for this method, the equipment requires regular washing with water to remove salts formed from the neutralization reaction. Additionally, this method requires an accumulator to remove the amines and the wash water.